Semiconductor integrated circuit system with termination circuit

ABSTRACT

A semiconductor integrated circuit is described. A transmitter-receiver transmits and receives data to and from outside by a first external terminal and transmits a first control signal by a second external terminal. When another data is transmitted after the data is transmitted and when a data transmission interval from a time when the data is transmitted to a time when the another data is transmitted is equal to or smaller than a first threshold, the transmitter-receiver continuously outputs, from the first external terminal, a potential level of about ½of a potential level obtained by adding a first potential level and a second potential level, during the data transmission interval, and changes the second potential level of the first control signal to the first potential level when the data transmission interval exceeds the first threshold.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of Ser. No. 15/684,461, filed Aug.23, 2017, which is a continuation of application Ser. No. 15/016,594,filed Feb. 5, 2016, now U.S. Pat. No. 9,767,884, which is a continuationof application Ser. No. 14/579,364, filed Dec. 22, 2014, now U.S. Pat.No. 9,286,958, which is a continuation of application Ser. No.14/031,462, filed Sep. 19, 2013, now U.S. Pat. No. 8,952,719, issuedFeb. 10, 2015, which is a continuation of application Ser. No.13/271,819, filed Oct. 12, 2011, now U.S. Pat. No. 8,558,572, issuedOct. 15, 2013, which is a continuation of application Ser. No.12/876,747, filed Sep. 7, 2010, now U.S. Pat. No. 8,102,186, issued Jan.24, 2012, and related to application Ser. No. 12/876,760, filed Sep. 7,2010, now U.S. Pat. No. 8,253,436; issued Aug. 28, 2012, applicationSer. No. 12/876,793, filed Sep. 7, 2010, now U.S. Pat. No. 7,999,572,issued Aug. 16, 2011; and application Ser. No. 13/172,199, filed Jun.29, 2011, now U.S. Pat. No. 8,653,851; issued Feb. 18, 2014, and basedupon and claims the benefit of priority from Japanese Patent ApplicationNo. 2009-206881, filed Sep. 8, 2009, which are incorporated herein byreference in their entirety. This application claims only subject matterdisclosed in the parent application and therefore presents no newmatter.

BACKGROUND

1. Field of the Invention

The present invention relates to a semiconductor integrated circuit, andmore particularly, to a semiconductor integrated circuit suitable forpower-supply noise reduction.

2. Description of Related Art

In a semiconductor integrated circuit, there has been a problem thatdata transmission between transmitter-receivers is not accuratelyexecuted when power-supply noise occurs on signal lines used for thedata transmission between the transmitter-receivers. To reduce thepower-supply noise, reducing the impedance of the signal lines has beenrequired.

Therefore, a countermeasure, for example, ODT (On Die Termination)technique has been provided to reduce the power-supply noise on signallines used for data reception of transmitter-receivers (JEDEC STANDARD,DDR2 SDRAM SPECIFICATION JESD79-2E (Revision of JESD79-2D), April 2008,JEDEC SOLID STATE TECHNOLOGY ASSOCIATION). Specially, a bidirectionalsignal line for bidirectionally transmitting data between thetransmitter-receivers is equipped with a termination circuit whichswitches on an ODT function when receiving the data and switches off theODT function when not receiving the data in each transmitter-receiver.

SUMMARY

However, in the related art, in the case of data transmission betweenthe transmitter-receivers through the bidirectional signal line, thepower-supply noise occurs on the bidirectional signal line due to asudden fluctuation of a power supply voltage when the receiver circuit,which is a data receiving side, switches off the ODT function afterreceiving data. When the receiver circuit switches the ODT function fromthe off-state to the on-state to receive another data before thepower-supply noise converges, another data is influenced by thepower-supply noise. The present inventors have found a problem in therelated art that, as described above, it is impossible to executetransmission and reception of data accurately.

A first exemplary aspect of the present invention is a semiconductorintegrated circuit including:

first and second transmitter-receivers that execute transmission andreception of data through a signal line, in which

the first transmitter-receiver includes:

-   -   a first termination circuit that includes a first resistor and a        first switch, the first resistor being provided between a first        power supply terminal and the signal line, the first switch        controlling a current flowing through the first resistor to be        turned on and off; and    -   a control circuit that outputs a first control signal to the        first termination circuit so that the first switch is turned on        when the first transmitter-receiver receives data, the first        switch is turned off when the first transmitter-receiver        transmits the data, and the first switch is continuously on        during a first predetermined period after receiving the data        when the first transmitter-receiver further receives another        data after receiving the data.

With the circuit structure as described above, it is possible to executetransmission and reception of data accurately by reducing thepower-supply noise.

According to an exemplary aspect of the present invention, it ispossible to provide a semiconductor integrated circuit capable ofexecuting transmission and reception of data accurately.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other exemplary aspects, advantages and features will bemore apparent from the following description of certain exemplaryembodiments taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a semiconductor integrated circuit according to afirst exemplary embodiment of the present invention;

FIG. 2 illustrates the semiconductor integrated circuit according to thefirst exemplary embodiment of the present invention;

FIG. 3 is a timing chart depicting an operation of the semiconductorintegrated circuit according to the first exemplary embodiment of thepresent invention; and

FIG. 4 illustrates a semiconductor integrated circuit according to asecond exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Specific exemplary embodiments of the present invention are described indetail below with reference to the drawings. The same components aredenoted by the same reference numerals in the drawings, and for clarityof explanation, repeated explanation is omitted as appropriate.

[First Exemplary Embodiment]

Referring to the drawings, a semiconductor integrated circuit accordingto a first exemplary embodiment of the present invention will bedescribed. The present invention can be applied to a circuit whichincludes a first transmitter-receiver, a second transmitter-receiver,and a signal line for bidirectionally transmitting data between thefirst transmitter-receiver and the second transmitter-receiver(hereinafter, referred to simply as “bidirectional signal line”), andhas an ODT function. In this exemplary embodiment, a case is explainedhereinafter in which the circuit shown in FIG. 1 includes an SoC (Systemon Chip) circuit and an SDRAM (Synchronous Dynamic Random Access Memory)circuit, and data transmission is executed between the SoC circuit andthe SDRAM circuit through the bidirectional signal line.

FIG. 1 illustrates a semiconductor integrated circuit according to thefirst exemplary embodiment of the present invention. The circuit shownin FIG. 1 includes an SoC circuit (first transmitter-receiver) 100 andan SDRAM circuit (second transmitter-receiver) 101. Data transmission isexecuted between the SoC circuit 100 and the SDRAM circuit 101 in theDDR (double data rate) mode.

First, the circuit structure of the semiconductor integrated circuitaccording to the first exemplary embodiment of the present inventionwill be described. The SoC circuit 100 outputs a 2-bit clock signal CKand a 2-bit clock signal CKB, which is a differential signal of theclock signal CK, to the SDRAM circuit 101. The SoC circuit 100 furtheroutputs a 16-bit control signal CMD, which includes commands for eachaddress of the SDRAM circuit 101, to the SDRAM circuit 101. Note thatthe SDRAM circuit 101 receives the control signal CMD in synchronizationwith the clock signals CK and CKB.

Each of 32-bit data DQ, a 4-bit strobe signal DQS, and a 4-bit strobesignal DQSB, which is a differential signal of the strobe signal DQS, isbidirectionally transmitted and received between the SoC circuit 100 andthe SDRAM circuit 101. A receiver circuit, which is one of the SoCcircuit 100 and the SDRAM circuit 101, receives the data DQ insynchronization with the strobe signals DQS and DQSB. Note that thesignal names described above also represent the corresponding signalline names.

The circuit shown in FIG. 2 shows a 1-bit bidirectional signal line,which is one of strobe signal lines DQS[3:0] and DQSB[3:0] and a datasignal line DQ[31:0], and corresponding peripheral circuits of thecircuit shown in FIG. 1. In this exemplary embodiment, a case isexplained hereinafter in which the 1-bit bidirectional signal line isthe data signal line DWI The data signal line DQ[0] is connected betweenthe SoC circuit 100 and the SDRAM 101 as described above.

The SoC circuit 100 includes an external terminal 201, a buffer 202, abuffer 203, a termination circuit (first termination circuit) 204 whichhas an ODT function, a control circuit 205 which outputs a controlsignal (first control signal) 200 to control the ODT function of thetermination circuit 204 to be turned on and off, and an inverter 206.The termination circuit 204 includes a resistor (first resistor) 207, aresistor 208, a switch (first switch) 209, and a switch 210. In thisexemplary embodiment, a case is explained in which the switch 209 is aP-channel MOS transistor and the switch 210 is an N-channel MOStransistor.

In the SoC circuit 100, the data signal line DQ[0] is connected to aninput terminal of the buffer 202 and an output terminal of the buffer203 through the external terminal 201.

The termination circuit 204 is provided between the external terminal201 and the buffer 202. In the termination circuit 204, the switch 209and the resistor 207 are connected in series between a high potentialside power supply terminal VDD and a node N1 which is located on thesignal line connecting the external terminal 201 and the buffer 202. Theswitch 210 and the resistor 208 are connected in series between a lowpotential side power supply terminal VSS and the node N1. In otherwords, the source terminal of the switch 209 is connected to the highpotential side power supply terminal VDD. The drain terminal of theswitch 209 is connected to one terminal of the resistor 207. The otherterminal of the resistor 207 is connected to one terminal of theresistor 208. The other terminal of the resistor 208 is connected to thedrain terminal of the switch 210. The source terminal of the switch 210is connected to the low potential side power supply terminal VSS. Theother terminal of the resistor 207 and one terminal of the resistor 208are commonly connected to the node N1. Note that the switch 209 and theresistor 207 which are connected in series between the high potentialside power supply terminal VDD and the node N1 may be switched around.Similarly, the switch 210 and the resistor 208 which are connected inseries between the low potential side power supply terminal VSS and thenode N1 may be switched around.

An output terminal of the buffer 202 is connected to an input terminalIN of the control circuit 205. An input terminal of the buffer 203 isconnected to an output terminal OUT of the control circuit 205. Anoutput terminal C1 of the control circuit 205 is connected to the gateterminal of the switch 209 and the gate terminal of the switch 210through the inverter 206. Such a peripheral circuit configuration isalso employed in the other bidirectional signal lines. Note that thecontrol circuit 205 is commonly provided to these bidirectional signallines.

Next, the operation of the semiconductor integrated circuit according tothe first exemplary embodiment of the present invention will bedescribed. A case is explained hereinafter in which the SoC circuit 100receives (reads) the data such as the data DQ and the strobe signals DQSand DQSB transmitted from the SDRAM circuit 101. First, the SoC circuit100 outputs the control signal CMD to the SDRAM circuit 101. After that,for example, the SDRAM circuit 101 transmits the data DQ stored in amemory area of an address specified by the control signal CMD, and thestrobe signals DQS and DQSB to the SoC circuit 100. In this case, thedata DQ transmitted from the SDRAM circuit 101 has a predetermined burstlength.

The SoC circuit 100 receives each signal output from the SDRAM circuit101 through the corresponding signal line, external terminal 201, andbuffer 202. Note that the SoC circuit 100 receives the data DQ insynchronization with the strobe signals DQS and DQSB. The data DQreceived by the SoC circuit 100 is input to the control circuit 205 andthe other peripheral circuits (not shown). A period between the timewhen the SoC circuit 100 starts to transmit the control signal CMD andthe time when the SoC circuit 100 starts to receive the correspondingdata DQ is called a read latency (RL).

When receiving the data transmitted from the SDRAM circuit 101, the SoCcircuit 100 controls the ODT function of the corresponding terminationcircuit 204 to be turned on to reduce power-supply noise occurring onthe data signal line DQ and the strobe signal lines DQS and DQSB.Specifically, the SoC circuit 100 controls the switches 209 and 210,which are provided in the corresponding termination circuit 204, to beturned on based on the control signal (first control signal) 200 fromthe control circuit 205 and sets the node on the corresponding signalline to a predetermined potential (for example, one-half of the highpotential side power supply voltage VDD). This makes it possible for theSoC circuit 100 to receive the data accurately by reducing thepower-supply noise included in the received data.

A case is explained hereinafter in which the SoC circuit 100 transmits(writes) the data to the SDRAM circuit 101. First, the SoC circuit 100outputs the control signal CMD to the SDRAM circuit 101. After that, theSoC circuit 100 transmits the data DQ and the strobe signals DQS andDQSB to the SDRAM circuit 101. In this case, the data DQ transmittedfrom the SoC circuit 100 has a predetermined burst length.

Then, the SDRAM circuit 101 receives the data DQ in synchronization withthe strobe signals DQS and DQSB. For example, the data DQ is writteninto the memory area of the address specified by the control signal CMD.A period between the time when the SoC circuit 100 starts to transmitthe control signal CMD and the time when the SoC circuit 100 starts totransmit the corresponding data DQ is called a write latency (WL).

When transmitting the data to the SDRAM circuit 101, the SoC circuit 100controls the ODT function of the corresponding termination circuit 204to be turned off. Specifically, the SoC circuit 100 controls theswitches 209 and 210, which are provided in the correspondingtermination circuit 204, to be turned off based on the control signal200 from the control circuit 205, thereby preventing the potential ofthe data transmitted to the SDRAM circuit 101 through the buffer 203 andthe external terminal 201 from being decayed. This makes it possible forthe SoC circuit 100 to transmit the data accurately.

In this manner, the SoC circuit 100 switches between a read mode inwhich the SoC circuit 100 receives the data transmitted from the SDRAMcircuit 101 and a write mode in which the SoC circuit 100 transmits thedata to the SDRAM circuit 101, based on the control signal CMD. Notethat the SoC circuit 100 outputs the control signal CMD which has a datalength corresponding to one cycle of the clock signal CK atpredetermined time intervals.

For example, the SoC circuit 100 receives data such as the data DQ inthe read mode or transmits the data in the write mode, and after thepredetermined time interval, receives or transmits another data in thesame mode. Alternatively, the SoC circuit 100 receives data such as thedata DQ in the read mode or transmits the data in the write mode, andafter the predetermined time interval, receives or transmits anotherdata in a different mode. The data transmission and reception asdescribed above is repeated.

The SoC circuit 100 according to this exemplary embodiment exhibitscharacteristics when the SoC circuit 100 receives data such as the dataDQ in the read mode, and after the predetermined time interval, receivesanother data in the read mode again. The operation of the SoC circuit100 in this case will be described with reference to FIG. 3.

First, the SoC circuit 100 outputs the control signal CMD (which isindicated by “A” shown in FIG. 3 and is hereinafter referred to as “readcommand A”) to the SDRAM circuit 101. Then, the SDRAM circuit 101transmits the data DQ (“D” shown in FIG. 3), which has a predeterminedburst length, and the corresponding strobe signals DQS and DQSB to theSoC circuit 100 after the period of the read latency RL (“C” shown inFIG. 3).

In this case, when receiving the data through the bidirectional signallines (the data signal line DQ and the strobe signal lines DQS andDQSB), the SoC circuit 100 controls the ODT function of thecorresponding termination circuit 204 to be turned on.

After outputting the read command A, the SoC circuit 100 outputs a readcommand E (“E” shown in FIG. 3) after the period of the predeterminedtime interval (“B” shown in FIG. 3). The SDRAM circuit 101 transmits thedata DQ (“G” shown in FIG. 3), which has a predetermined burst length,and the corresponding strobe signals DQS and DQSB to the SoC circuit 100after the period of the read latency RL (“F” shown in FIG. 3)

In this case, the control circuit 205 provided in the SoC circuit 100calculates a period (H), in which the data DQ is not transmitted, basedon the interval (B) of the read commands (A, E), the read latency RL (C,F), and the burst length (D, G) of the data DQ. Based on the period thusobtained, the control circuit 205 determines whether to turn off the ODTfunction of the termination circuit 204 during the period (H) in whichthe data DQ is not transmitted. Then, the control circuit 205 outputsthe control signal 200 to the termination circuit 204 based on theresults of the determination. When the period (H) is less than or equalto a predetermined threshold, the termination circuit 204 causes the ODTfunction to be continuously on during the period (H) (“I” shown in FIG.3). When the period (H) exceeds the predetermined threshold, thetermination circuit 204 switches off the ODT function during the period(H).

In the case where the read mode is repeated, when the terminationcircuit 204 causes the ODT function to be continuously on during theperiod in which the data transmission is not executed, power-supplynoise, which may occur due to switching from the on-state to theoff-state of the ODT function, does not occur on the bidirectionalsignal line corresponding to the termination circuit 204. Therefore, itis possible for the SoC circuit 100 to receive the data accurately byreducing the power-supply noise which has been a problem in the relatedart.

In the case where the read mode is repeated, when the period (H) inwhich the data transmission is not executed exceeds the threshold, thetermination circuit 204 switches the ODT function from the on-state tothe off-state during the period in which the data transmission is notexecuted. In other words, the SoC circuit 100 can control the ODTfunction of the termination circuit 204 to be switched from theoff-state to the on-state again after a lapse of a period sufficient forconverging the power-supply noise due to switching from the on-state tothe off-state of the ODT function. This makes it possible for the SoCcircuit 100 to receive the data accurately by reducing the effect of thepower-supply noise. Note that the timing of switching from the on-stateto the off-state of the ODT function may be arbitrarily determined aslong as the power-supply noise is converged by the time when the nextdata reception starts.

As described above, in the case where the receiver circuit (for example,the SoC circuit 100) continuously receives data, the semiconductorintegrated circuit according to this exemplary embodiment of the presentinvention controls the ODT function of the receiver circuit to be turnedon and off based on a data reception interval. In other words, thesemiconductor integrated circuit according to this exemplary embodimentcontrols the ODT function of the receiver circuit to be continuously onor to be switched from the on-state to the off-state. This makes itpossible for the semiconductor integrated circuit according to thisexemplary embodiment to execute transmission and reception of dataaccurately by reducing the effect of the power-supply noise.

[Second Exemplary Embodiment]

In the first exemplary embodiment, the case has been explained in whichthe SoC circuit 100 includes the termination circuit 204. Meanwhile, inthis exemplary embodiment, a case is explained in which an SDRAM circuitalso includes a termination circuit.

Referring to FIG. 4, an SDRAM circuit 102 which corresponds to the SDRAMcircuit 101 shown in FIG. 2 further includes a termination circuit(second termination circuit) 215. FIG. 4 shows the 1-bit bidirectionalsignal line, which is one of the strobe signal lines DQS[3:0] andDQSB[3:0] and the data signal line DQ[31:0], and the correspondingperipheral circuits.

The circuit shown in FIG. 4 includes the SoC circuit 100 and the SDRAMcircuit 102. The SDRAM circuit 102 includes an SDRAM unit 211, anexternal terminal 212, a buffer 213, a buffer 214, a termination circuit215, and an inverter 216. The termination circuit 215 includes aresistor (second resistor) 217, a resistor 218, a switch (second switch)219, and a switch 220. The circuit structure and the operation of theSoC circuit 100 are the same as those of the first exemplary embodiment,so the description thereof is omitted. As for the connections and theoperations of circuits which are associated with the ODT function andprovided in the SDRAM circuit 102, only different contents from those ofthe SoC circuit 100 will be described.

When receiving the data transmitted from the SoC circuit 100, the SDRAMcircuit 102 controls the ODT function of the corresponding terminationcircuit 215 to be turned on to reduce the power-supply noise occurringon the data signal line DQ and the strobe signal lines DQS and DQSB.Specifically, the SDRAM circuit 102 controls the switches 219 and 220,which are provided in the corresponding termination circuit 215, to beturned on based on a control signal (second control signal) 221 from thecontrol circuit 205 and sets the node on the corresponding signal lineto the predetermined potential (for example, one-half of the highpotential side power supply terminal VDD). This makes is possible forthe SDRAM circuit 102 to receive the data accurately by reducing thepower-supply noise included in the received data.

When transmitting the data to the SoC circuit 100, the SDRAM circuit 102controls the ODT function of the corresponding termination circuit 215to be turned off. Specifically, the SDRAM circuit 102 controls theswitches 219 and 220, which are provided in the correspondingtermination circuit 215, to be turned off based on the control signal221 from the control circuit 205, thereby preventing the potential ofthe data transmitted to the SoC circuit 100 through the buffer 214 andthe external terminal 212 from being decayed. This makes it possible forthe SDRAM circuit 102 to transmit the data accurately. In addition, theconnections and the operations of circuits, which are associated withthe ODT function and provided in the SDRAM circuit 102, are the same asthose of the first exemplary embodiment, so the description thereof isomitted.

With this circuit configuration, in the case where data transmissionbetween the transmitter-receivers through the bidirectional signal, thesemiconductor integrated circuit according to this exemplary embodimentcan execute transmission and reception of data accurately by controllingthe ODT function of the receiver circuit even if either one of thetransmitter-receivers operates as the receiver circuit.

Note that the present invention is not limited to the above exemplaryembodiments, but can be modified as appropriate within the scope of thepresent invention. For example, though the above-mentioned exemplaryembodiments have described an example in which the semiconductorintegrated circuit includes a single SDRAM circuit, the presentinvention is not limited thereto. The semiconductor integrated circuitaccording to the present invention is also applicable to a circuitconfiguration including a plurality of SDRAM circuits.

Though the above-mentioned exemplary embodiments have described anexample in which, when the receiver circuit (for example, the SoCcircuit 100) continuously receives data, the control circuit 205 outputsthe control signal (for example, the control signal 200) based on theinterval of the address command such as a read command, the read latencyRL, and the burst length of the data DQ, the present invention is notlimited thereto. The present invention is also applicable to a circuitconfiguration for outputting the control signal (for example, thecontrol signal 200) based on at least one of the above-mentioned piecesof information (for example, the interval of the address command) if itis possible to control the ODT function based on the data receptioninterval.

Moreover, the termination circuit is not limited to the circuitsillustrated in the above-mentioned exemplary embodiments. The presentinvention is also applicable to a circuit configuration including aresistor and a switch which are connected in series between the powersupply terminal (first power supply terminal) having the predeterminedpotential (for example, one-half of the high potential side power supplyvoltage VDD) and the node on the corresponding bidirectional signalline.

The first and second exemplary embodiments can be combined as desirableby one of ordinary skill in the art.

While the invention has been described in terms of several exemplaryembodiments, those skilled in the art will recognize that the inventioncan be practiced with various modifications within the spirit and scopeof the appended claims and the invention is not limited to the examplesdescribed above.

Further, the scope of the claims is not limited by the exemplaryembodiments described above.

Furthermore, it is noted that, Applicant's intent is to encompassequivalents of all claim elements, even if amended later duringprosecution.

What is claimed is:
 1. A semiconductor integrated circuit system,comprising: a first termination circuit; a first transmitter-receiver; asecond termination circuit; and a second transmitter-receiver, whereinwhen transmitted data from the second transmitter-receiver is receivedby the first transmitter-receiver, the second termination circuit isinactivated, when the data is transmitted to the secondtransmitter-receiver by the first transmitter-receiver, the secondtermination circuit is activated, and when another data is transmittedfrom the first transmitter-receiver to the second transmitter-receiverafter the data is transmitted from the first transmitter-receiver to thesecond transmitter-receiver, when a data transmission interval from atime when the data is transmitted to a time when the another data istransmitted is equal to or smaller than a first threshold, theactivation of the second termination circuit is maintained, and when thedata transmission interval exceeds the first threshold, the secondtermination circuit is inactivated.
 2. The semiconductor integratedcircuit system according to claim 1, wherein the firsttransmitter-receiver is connected to the second transmitter-receiverthrough an external terminal.
 3. The semiconductor integrated circuitsystem according to claim 1, wherein the data transmission interval isdetermined in accordance with a write latency of the transmitted datafrom the first transmitter-receiver to the second transmitter-receiverand a write latency of the subsequently-transmitted another transmitteddata.
 4. The semiconductor integrated circuit system according to claim1, wherein each of the transmitted data from the firsttransmitter-receiver to the second transmitter-receiver and thesubsequently-transmitted another transmitted data is burst data, eachhaving a predetermined burst length, and the data transmission intervalis determined in accordance with the burst lengths.
 5. The semiconductorintegrated circuit system according to claim 1, wherein the secondtermination circuit is controlled by the first transmitter-receiver. 6.The semiconductor integrated circuit system according to claim 1,wherein when the transmitted data from the second transmitter-receiveris received by the first transmitter-receiver, the first terminationcircuit is activated, when the data is transmitted to the secondtransmitter-receiver by the first transmitter-receiver, the firsttermination circuit is inactivated, and when another data is received bythe first transmitter-receiver from the second transmitter-receiverafter the data is received by the first transmitter-receiver from thesecond transmitter-receiver, when a data reception interval from a timewhen the data is received to a time when the another data is received isequal to or smaller than a second threshold, the activation of the firsttermination circuit is maintained, and when the data reception intervalexceeds the second threshold, the first termination circuit isinactivated.
 7. The semiconductor integrated circuit system according toclaim 6, wherein the data reception interval is determined in accordancewith a period between a time when the first transmitter-receiver outputsa command for receiving data to the second transmitter-receiver and atime when the first transmitter-receiver further outputs a command forreceiving the another data.
 8. The semiconductor integrated circuitsystem according to claim 6, wherein the data reception interval isdetermined in accordance with a latency between a time when the firsttransmitter-receiver outputs a command for receiving data to the secondtransmitter-receiver and a time when the first transmitter-receiverstarts to receive the data.
 9. The semiconductor integrated circuitsystem according to claim 6, wherein the data received by the firsttransmitter-receiver is burst data, and the data reception interval isdetermined in accordance with a burst length of the received data. 10.The semiconductor integrated circuit system according to claim 6,wherein the second transmitter-receiver is a SDRAM, and the firsttransmitter-receiver is a controller that controls the SDRAM.